1. Field of the Invention
This invention relates to a scroll sawing machine, more particularly to a scroll sawing machine with a speed ratio varying device for a transmitting shaft which is driven to rotate by an output shaft of a motor so as to effectuate reciprocating upward and downward movements of a saw blade.
2. Description of the Related Art
Referring to FIGS. 1 to 3, a conventional scroll sawing machine 10 is shown to include a machine frame 11, a table 17, a hollow blade-holding frame 12, a saw blade 163, a motor 13, a blade-driving member 14, and a table-adjusting member 18.
The blade-driving member 14 includes upper and lower arms 141, 142 which respectively extend along upper and lower frame portions 122, 123 of the blade-holding frame 12 and which have distal ends projecting outwardly for coupling with the saw blade 163 by means of upper and lower mounting seats 161, 162, and a linking lever 143 which is disposed in a connecting frame portion 121 of the blade-holding frame 12 and which is pivoted to the upper and lower arms 141, 142.
The motor 13 is mounted on a motor seat 132 which is disposed in the connecting frame portion 121 of the blade-holding frame 12, and has an output shaft 131 on which a pulley 151 of a transmitting unit 15 is sleeved. The transmitting unit 15 has a cam wheel 152 mounted rotatably on the motor seat 132, and a belt 153 trained on the pulley 151 and the cam wheel 152 such that rotation of the pulley 151 is transmitted to rotate the cam wheel 152 to permit a cam portion 154, which is eccentrically mounted on the cam wheel 152 and which engages a slot 1551 in a cam follower 155 of the linking lever 143, to guide the cam follower 155 so as to perform reciprocating upward and downward movements of the upper and lower arms 141, 142.
However, the rotational speed of the cam wheel 152 is fixed, thereby resulting in unchangeable sawing speed of the saw blade 163 for sawing workpieces of different thickness. Thus, the service life of the saw blade 163 may be shortened, and the sawing quality of the workpiece may be adversely affected.